Allosaurus was a large (up to 9.7 m long) bipedal (moving on two legs), carnivorous dinosaur that lived during the late Jurassic period, 155 to 145 million years ago.
Allosaurus was named by famous palenotologist O. C. Marsh, who found the type species during the famed competition with E. D. Cope.
The name Allosaurus comes from the Greek allos/?????, meaning "strange" or "different" and saurus/??????, meaning "lizard" or "reptile" (Liddell and Scott 1987).
The same team later excavated a second Allosaurus, "Big Al Two," which is the best preserved skeleton of its kind to date.
The closely related genus Saurophaganax (OMNH 1708) reached 10.9 m (36 ft) in length, and has sometimes been included in the genus Allosaurus as Allosaurus maximus.
The skeleton of Allosaurus, like other theropods, displayed bird-like features, such as a furcula (wishbone) and neck vertebrae hollowed by air sacs.
Several gigantic specimens have been attributed to Allosaurus, but may in fact belong to other genera.
The material from the Cleveland Lloyd Dinosaur Quarry specimen is much smaller and more lightly-built than the huge and robust Allosaurus from Brigham Young University's Dry Mesa Quarry.
The most distinctive feature of Allosaurus was a pair of blunt horns, just above and in front of the eyes.
The first Allosaurus fossil to be described was a "petrified horse hoof" given to Ferdinand Vandiveer Hayden in 1869, by the natives of Middle Park, near Granby, Colorado.
One species of Allosaurus has been described from Portugal, A. europaeus (Mateus et al.
Along with its distant relative Tyrannosaurus, Allosaurus has come to represent the quintessential large, carnivorous dinosaur in popular culture.
Allosaurus is the most common theropod fossil in the vast tract of dinosaur-bearing rock of the American Southwest known as the Morrison Formation.
Allosaurus has been featured in such films as The Lost World, One Million Years B.C.E., The Valley of Gwangi, A Sound of Thunder, and others.
The animal had an average length of 7-9 meters (~30 feet), with the largest definitive Allosaurus specimen (AMNH 680) measuring 9.7 m (32 ft).
Allosaurus shared the landscape with several genera of giant sauropods such as Apatosaurus, Diplodocus, and Camarasaurus as well as other herbivores such as Stegosaurus and Camptosaurus, all of which may have been potential prey.
Allosaurus was a typical large theropod, having a massive skull on a short neck, a long tail, and reduced forelimbs.